Twt arcing suppressor using temporary shunting thyratron and long duration disablingcircuit



3,084,284 YRATRoN Filed Dec. 30, 1959 April 2, .1963 H. R. SCHUL-rz, SR.. ET AL TwT AROING suPPREssOR USING TEMPORARY sHuNTTNG TH AND LONG DURATION DTSABLINO CIRCUIT United States Patent O TWT ARClNG SUPPRESSR USENG TEMPGRARY SHUNTENG THYRATRN AND LNG DURA- 'llGN DSAEHNG Cillll'll Harold ist. Schultz, Sr., Los Angeles, and Robert E.

Mason, Costa Mesa, tCali., assgnors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Dec. 3G, i959, Ser. No. 863,032 6 Claims. (Cl. 328-9) This invention relates to overload protection circuits and particularly to a circuit for high speed control of -a high voltage during short circuit or arcing conditions of the circuit being protected.

lt is well known that with electronic equipment, relatively high voltages are sometimes required such as in biasing traveling wave tubes with a high cathode voltage. In the presence of a defect or a short circuit condition such as m'cing in a traveling wave tube, the high voltages can destroy the tube -in a very short period of time. It is, thus, necessary to provide a voltage protection means that reduces a high voltage to -a relatively lower voltage in `as small an elapsed time as possible in order to adequately protect electronic equipment using very high voltages such as required in traveling Wave tubes.

Previous methods are yfound to be generally too slow and unreliable to provide adequate protection to some electronic ydevices against short circuit and arcing lconditions at very high voltages. Also, switching circuits of the prio-r art `are expensive, bulky and unreliable because of the large number of parts subject to failure. Relays are used to provide overload protection but relay 4devices have a mechanical limit placed on the time in which they can periorm their desired function. A physically large relay is required to handle large voltages Vand currents resulting in a long transit time of the mechanical moving parts.

Fuse devices are relatively slow because of the time required to melt the fuse material and because of the large arc developed lwhen disconnecting a large voltage. Also, =a fuse does not allow power to be :automatically reapplied after the occurrence or a short circuit condition.

A simple and reliable system that would disconnect high voltages at a very high speed would be very valuable to the art. Also, a system that provides automatic reduction of a `bias potential during temporary short circuit conditions and further provides a means to permanently disconnect the bias potential during permanent Ashort circuit conditions would greatly reduce the maintenance problem.

With grid controlled traveling wave tubes, the high voltage potential is applied from the anode and collector to the cathode, and pulsing operation is produced by applying pulses to the grid. Control grids are provided in traveling wave tubes so that pulsing may `be carried out atp. relatively low voltage thus saving the `weight of modulating equipment required to pulse the high voltage between the anode and cathode. Because of the presence or the grid, short circuits or arcs are especially prevalent between the grid and anode of this type of traveling wave tube. Thus, a high voltage protection means to temporarily lower the voltage to remove or suppress an arc is especially required to protect grid controlled traveling wave tubes.

lt is, therefore, 'an object of this invention to provide a voltage control circuit lthat provides high speed control of a high voltage applied to an electronic device.

lt is a further object of this invention to provide a high voltage control circuit that operates at suflicient speed to protect a traveling wave tube from damage during an arcing condition.

hidi Patented Apr. 2, ld

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It is 'a still 'further object of this invention to provide a simplied voltage control system that reduces the supply voltage during short period overload conditions land automatically reapplies the high voltage at the termination yof a very short period.

It is another object of this invention to provide a simplified and reliable control system that not only responds to a short circuit condition such as arcing to temporarily reduce the supplied voltage to allow the arc to be terminated, but when the short ycircuit conditions lcontinue yto occur :a pre-selected number of times, permaw nently disconnects the voltage supply.

Briefly, this invention is a voltage control system that protects devices such as grid controlled traveling wave tubes from damage during high voltage short circuits lsuch as arcing. A thyratron is provided with its anode to cathode path coupled across the positive to negative terminals of a traveling wave tube and its grid responsive to the output pulse of a blocking oscillator. The blocking oscillator is responsive to an increase of the potential at the low voltage terminal of the traveling wave tube indicating an increase of current through the cathode of the traveling-wave tube resulting from an arcing condition, to bias the thyratron into conduction so as to provide a low impedance shunt path for current yfrom the power supply. The storage capacitance in the pov/er supply thus rapidly discharges through the thyratron so that the high voltage is temporarily reduced through the traveling wave tube to terminate the :arcing condition. The reduced voltage also deionizes the thyrat-ron biasing it out of conduction and automatically restoring the traveling wave tube to normal operation. To provide a means for permanently disconnecting the power supply `during a pre-selected number of short circuits, a diode is coupled to the cathode of the thyratron and to ground through a sensing capacitor which is charged during each short circuit condition. The sensing capacitor is coupled in parallel with a disabling relay land a gas tube so that when the capacitor is charge an amount indicative of the pre-selected number of short circuits, the disabling lrelay is activated which in turn permanently disconnects the power supply. Thus, a system is provided that automatically restores operation `during random `arcing `conditions, but permanently disconnects the high voltage from the ftube when repetitive arcing is present.

The novel features of this invention, as well as the invention itself, 4both as to its organization and method of operation, will best be understood from the accom.- panying description, taken in connection with the accompanying drawing in which:

The sole FIGURE is a schematic circuit diagram of a voltage control system in accordance with this invention.

Referring to the ligure, a power supply lil is provided to supply a high voltage to 'a traveling wave tube 12. The power supply l0 may include an AC. (alternating current) powerl source 14 supplying A.C. power to a primary winding 16 of a transformer l8r. The cur-rent path through the primary winding 16 may include a `switch 22 of a relay 2d, the switch 22 being normally closed until the relay 20 is energized to fopen the switch 22, at which time the switch 22 remains open until the relay Ztl' yis manually reset, for example. The transformer llly includes a secondary winding 2d for applying a high voltage to a rectier 26 lthat has one output terminal referenced to a supply lead 34 through a current limiting inductor 36 and resistor 38. The rectilier 26 also has another output terminal that is referenced to a ground potential lead 28. The power supply 1d supplies a negative potential such as -l0,000 volts to the supply lead 34. Coupled between 'the leads 28 and 34 is a capacitor itl that provides filterling and functions as la reservoir to supply peak current for pulsed yoperation of the traveling Wave tube 12, which capacitor arrangement is well known rin the art. The capacitor 40 is relatively large in value `so that a large peak current -may be provided With a relatively small transformer 18 and rectifier 26. It is to be noted that the power supply '10 may be any conventional power supply that provides means for storage of energy when the load, such as the traveling Wave 'tube 12 during pulsed operation, periodically utilizes current. A D-.C. 'generator, tor example, stores suicient energy to supply a high curren-t for short periods and m-ay be utilized in the A system of this invention. Also, the capacitor 40* may be electively coupled across the leads 28 and 34 in any desired position in the circuit.

The supply lead 34 applies a negative voltage to a cath-ode 44 yof the traveling Wave tube 12 which is shown for purposes of illustr-ation in a `grid controlled arnangement with an anode 50 biased at substantially a ground potential and a collector 51` grounded. The system of this invention is equally applicable to a tuaveling Wave tube arranged with the anode at -a high potential above ground and the cathode grounded. Also, the system of this invention is applicable to klystrons or other electronic devices that are subject to short circuit conditions such as arcing.

In the illustrated arrangement lof the traveling waive tube 12, a helix 46 has one end coupled to a termin-al 47 for receiving RF (radio frequency) energy and the other end coupled to an output terminal 49 for applying arnpliiied RF energy thereto. The anode 50 is biased from ground through a dropping resistor `52. A .grid 53 is controlled by pulses through a secondary winding 54 of an isolating transformer 56. The grid 53 is biased slightly negative with respect to lthe potential on the -supply lead 34 from -a negative bias supply 60. A pulse source 62 is provided to apply pulses through a primary winding 64 `of the transformer 56 for intermittedly biasing the traveling wave tube 12 into conduction. A cathode heater '65 is provided and is responsive to +110 volts A.C. from terminals 67. The cathode 44 is coupled by 2a lead 55 vto the supply lead 34 throu-gh a sensing resistor 68? and to ia sensing lead 70 to which is applied a Vsignal such las shown by a waveform 81 when current is increased thnough the cathode 44. The sensing lead 70 may also be arranged to obtain la signal from Van induc'taince element 4such as a torroid coil arranged wi-th the lead 55 passing therethrough and the sensing llead 70 'coupled to a winding Aaround the torroid, instead of utilizing a sensing resistor 68. A torroid coil `arrangement has the advantage that current now from the cathode I44 is hindered a minimum amount while the sening resistor 68 has the advantage that gradual voltage changes are sensed.

I't is to be recognized that when the traveling wave tube 12 is arranged with a grounded cathode `and `low voltage applied to the collector, the sensing lead 7()l maybe arranged to receive la signal from the collector. Also, with other electronic devices in which a high voltage is supplied, the sensing lead 70 may be appropriately arranged to sense a short circuit or arcing condition.

The sensing llead 70 applies a positive going signal to a blocking oscillator 72 that in turn controls va thyratron tube 74, which as is well known is a gas 1tube in which the grid initiates the anode current but generally does not limit the anode current. The `thyratron 74 which is normally nonconducting (NNC), has an anode on which Avis impressed ground potential from the ground lead 28 and has a cathode coupled to the supply lead 34 through a resistor 76. The thyrat-non 74 also includes a cathode `heater operated from llO volt A.C. terminals 78. Thus, Vwhen a posi-tive going signal is applied 'to the grid of the `-thyratron 74 from the blocking oscillator 72A, the thyratron 74 is biased into conduction and the gas therein is ionized. Thus, a low impedance path is provided between the ground lead 28 and 'the nega-tive supply lead 34 during a Vshort period before the potential on the cathode rises to dcionize the gas in the tube 74.

The blocking oscillator 72, which is shown as a conventional parallel triggered blocking oscillator, includes an Vamplifier tube having a grid responsive 'to a rise of the potential on the sensing lead 70 as shown by the waveform 81 through .a coupling capacitor 82. The grid of the amplifier tube 80 is biased through a current limiting resistor 84 by la bias supply 816, which for example may be a 5 volt source 'to reduce the grid bias 5 volts less than the negative potential on the supply lead 34.

The bias supply '86 may be variable potential source to control the dynamic range of the system by controlling the potential at Which the amplifier tube till` is biased into conduction. The amplifier tube Si) has a cathode biased to the negative 'supply lead y34 and an anode coupled to the anode of 'a blocking oscillator tube 88, which in turn has a cathode biased to the supply lead 34. 4A. transformer is provided with a Winding 492 having one end biased to a |-150 volt terminal 94 and the other end coupled to the anode of the tube 88. A Winding 96 is inductively coupled to the winding 92 and has one end biased to a -4 -volt terminal `98 and the other end Vcontrolling the grid of the blocking oscillator tube 88. -An output winding is provided inductively coupled to the windings 92 and 96 with one end coupled to a 20'` fvolt terminal 102 ,and the other end applying an output signal shown by a waveform 103 to a lead 104. The terminals 94, 98 and `102 are coupled to a plate and bias supply i105 that is referenced to the negative potential of the supply lead 34. The output lead 104 applies the pulse of the waveform 103 to the grid of the thyratron tube `'74- through an inducto'r 1tl6 and Va parallel coupled resistor 108. The blocking oscillator 72 provides amplification and a pulse of the waveform 103 that has `a steep leading edge for vtriggering the thyratron tube 74 into conduction. In response to the pulse of the waveform 103, the thyratron tube 74 is triggered to an ionized Vcondition to provide a low impedance path to ycurrent from the capacitor 40 for lowering the voltage on the supply lead 34 and removing an arc, for example, in the traveling wave tube i12. As the capacitor 40 discharges so that the voltage across the thyratron tube 74 decreases, the gas therein is deionized fand normal operation is automatically restored. This Voperation is the high speed short period disabling of the circuit to overcome a single arcing of the traveling `rwave tube 12.

y The arrangement to disconnect the power supply 10 `after a pre-selected 'number of arcing or short circuit con* lditions have occurred and have been overcome by the 'low impedance path through the thyratron tube 74, will now be explained. An isolating diode 11112 of a long duration disabling circuit 111 is provided with an 'anode' coupled to the cathode of the tube 74 ythrough `a lead .114 and a cathode coupled through a lead 115' to a ch-arging capacitor 116 which is in turn Acoupled to an adjusting resistor'i118. A movable tap 120 of the adjusting resistor v118 biases the resistor 1.18 to the potential on the lead 34. Coupled in parallel across the charging capacitor 116 is a winding 123 of a relay 124 with a gas tube `126, which may be of the unipolar type, coupled in series between the coil 123 and the end of the capacitor 116 coupled to the `adjusting resistor 11S. The gas tube =126 which is nor- 'mally nonconductive (NNC) is arranged so that when the capacitor 116 charges sufficiently, a positive potential on the lead 115 ionizes .the gas in tube 126 to discharge the capacitor through the winding 4123 and energize the relay 124.

When the relay 124 is energized, a switch 1128 is closed and a terminal 13,2 applies +30 volts through a lead i133 to .a winding y134 of the relay 20, thus tripping the relay 20, opening the switch 22 and disconnecting lthe power -supply 10 from the supply lead 34.

Now that the arrangement of the syste-m has been explained, the operation thereof will `be explained in further detail. During normal operation a potential such as -l0,000 volts may be substantially maintained on the supply lead 34, the required voltage being determined by the electronic device to which the voltage is applied such as the traveling wave tube l2.. In response to a pulse from the pulse source `di. applied to the grid 53, a stream of electrons lis transmitted from the cathode 44 through the grid 53, through an aperature in the anode Sti` and through the center of the helix i6 to the collector 51. Thus, as is well known in the art, energy may be transferred to an RF signal applied to the helix d6 at the terminal i7 to provide amplification of the signal at the terminal del.

ln the arrangement shown, the cathode le is maintained at the low voltage and the anode 5t) and the collector 5l are substantially grounded. Arcing has been found to occur between the anode Sil and the `grid 53 when any defect is present such las stray electrons being emitted from the cathode ed. Arcing may .also occur between the anode Sil and the shielding (not shown). Normal deviations in manufacture make it difficult to produce a traveling wave tube in which the electron gun including the cathode ifidoes not produce stray electrons at some time during the operating life of the tube. Another cause of arcing between the anode `Sil and the grid 53 is ionization of any gases in the traveling wave tube by cosmic rays which may occur in outer space applications of the tube, as in a satellite. A grid type traveling wave tube has been found to be a necessity for operations such .as in satellites where weight is an important factor. A traveling wave where the high potential between the collector and cathode is modulated requires heavy and bulky modulating equipment that is unsatisfactory in most space operation.

Thus, in the arrangement shown in accordance with this invention, the tube l2 is pulsed at .the grid 53 from a pulse source 6?; so that peak power may be developed by the tube during the occurrence of a pulse. rl'he pulse source d2. may be synchronized with the pulsing operation of a pulsed transmitter, for example. The voltage which may be 10,000 volts or higher is maintained across the traveling wave tube 11.2 during normal operation. However, once an arc is initiated the system of this invention goes into operation to remove the high lvoltage so as to remove the arc. As is well known, an arc once initiated is maintained and, if not rapidly controlled, results in destruction of the tube. This arcing may occur only occasionally as a result of a random action or of ionization, or the arcing may occur many times indicating a permanent defect. The system or this invention rapidly controls either a single or a permanent default.

When a short circuit such as an arc between the anode Si) and grid S3 occurs, the voltage on the lead 55 rises toward ground potential, developing a positive signal as shown by the Waveform 8l which is applied to the blocking oscillator 72 to start the blocking oscillator action. Thus, an eective feedback path for temporarily disconnecting the power supply is provided as shown by an arrow ma along the lead 79 and as shown by an arrow ltlla between the blocking oscillator 76 and the tube 74. When the signal of the Waveform 81 is applied to the grid of the amplifier tube till and rises to a required level, the tube Sii is biased into conduction applying a negative going pulse `to the anode of the tube SS. The leading edge of this negative going pulse is applied through the windings 92 and 96 to the grid of the tube SS as a positive signal.

To further describe the blocking oscillator action, as current starts to ilow through the winding 92, a magnetic iield is set up in the transformer 9d to induce a potential in the winding @d such that the end thereof as coupled to the grid of the tube de is positive. rl`his magnetic field builds up from zero to a maximum in direct proportion to the current passed through the anode of the ampliiier tube 33 and therefore induces a voltage at the grid of the tube S3. As the tube 8S draws current through its anode, the magnetic field in the transformer 9@ continues to build up until such time as the current through the anode of the tube dit reaches its maximum value. Shortly after this time, the field starts to collapse. As a result of the rise and collapse of the iield the pulse of the waveform 103 is developed, which pulse has a relatively large amplitude, compared to the waveform 81, and has a fast rise time for controlling the thyratron tube 74. By using a blocking oscillator the sensing resistor 68 coupled to the cathode d4 of the traveling wave tube l2 may be relatively small in value because a small signal will trigger the blocking oscillator 72. Also, the shape of the voltage of the waveform 1% is independent of the shape of the voltage riso of the waveform 8l on the sensing lead 70.

The signal of the waveform 103 is applied through the peaking inductor 106 with a minimum of delay to they grid of the thyratron tube 74, initiating conduction by ionizing the gas therein. Thus, a low impedance shunt path is provided across the traveling wave tube 12 bef tween the leads 34 and 23. The storage element in the power supply lt) such as the capacitor 40 is rapidly discharged through the tube 74 with a short fall time because of the low value of resistance present in the path. Because current is limited through the inductance 36, the potential on the supply lead 34 rapidly rises until the voltage across the thyratron tube '74 is reduced to a small Value so as to deionize the tube and again present a high impedance to current ilow therethrough. Also, the voltage across the traveling wave tube l2 is reduced so as to eliminate arcing in the traveling wave tube l2.

The pulse of the waveform N3 developed by the blocking oscillator 72 falls before this deionization occurs so that the potential drop between the anode and cathode of the thyratron tube 74 renders the tube nonconductive. Thus, the high potential is again applied across the traveling wave tube l2 and normal operation is restored. The discharge time of the capacitor 4G and the ionization time of the thyratron tube 74 are very small. Also, as is Well known, the delay time through the blocking oscillator 72 is a minimum. Thus, the high voltage is rapidly removed across the traveling wave tube 12 so as to prevent any damage thereto. Also, the deionization time of the thyratron tube 74 is very small so that normal operation is rapidly restored.

The above described operation protects the tube l2 during each arcing condition. However, when arcing occurs successively the long duration disabling circuit lll operates to disconnect the power supply lil from the traveling wave tube l2. During each arcing condition, the potential on the cathode of the thyratron tube 74 rises as a result of current passing through the resistor 76, and the diode M2 is biased into conduction to pass some charging current to the charging capacitor 116. This current is passed through the diode 112 only during the short period that the tube 74 is maintained in conduction because when the tube 74 is deionized, the neg".- tive supply potential is again impressed on the anode and cathode of the diode 112. The charging capacitor llo substantially maintains its charge, discharging only a small amount because of the small amount of leakage current present. Thus, the lead 2.11.5 becomes more positive each time a fault or arcing condition occurs. After `a pre-selected number of successive corrections of a short circuit condition, the capacitor 116 rcharges sufficiently to ionize the gas tube X26 and `current flows through the winding 123 to energize the relay 124;. The relay me applies +30 volts through a feedback path for permanently disconnecting the power supply as shown by an arrow 133e, to the relay Ztl which is in turn energized to open the switch 22 and disconnect the AC. source i4 from the lead 34. Thus, the power is disconnected from the traveling Wave tube l2 until the relay 2d is manually reset, for example.

The adjustable tap Mil is provided so that a desired bias Vis maintained on the terminal of the gas tube 125 connected thereto. Thus, the tap may be adjusted so that after a pre-selected number of arcs of the tube 12 and periods of conduction of the thyratron tube 74, the gas tube 126 will be biased into conduction to disconnect the power supply. Because of the leakage of the charging capacitor 116, the pre-selected number of arcing conditions must occur Within a calculated period to disconnect the power source. Thus, a selected number of defaults yof the traveling wave tube 12 indicating a permanent defect in its operation results in the power supply being disconnected to prevent a large number of short period arcs that would eventually destroy the tube. Because traveling wave tubes are expensive and diflicult to construct, the above arrangement has the advantage that the defect may be corrected at the end of a period of utilization.

It is to be noted that although the electronic device supplied with a potential and protected against short circuit conditions has been described as a grid controlled traveling tube, the principles of this invention are equally applicable to other traveling wave tube arrangements and to other electron devices such as :klystrons or magnetrons. It is also to be noted that the illustrated potentials are only for purposes of illustration and may be reversed where applicable.

Thus, there has been described a high voltage control system for supply-ing a high potential to an electronic device -that rapidly lowers the supplied voltage during the occurrence of a short circuit condition such as arcing. The system then automatically restores the high potential to resume normal operation. A long duration disabling circuit is provided that Vcharges a capacitor during each defect. When a pre-selected number of arcing conditions occur during a certain period, relay circuits are activated to permanently disconnect .the power source from the device being biased. This arrangement is especially applicable to overcome the problems of utilization of a grid ycontrolled traveling `wave tube where the supplied bias is maintained between the collector and cathode and pulsing is applied only to the grid so that an arcing condition once initiated -w-ill be maintained to destroy the tube.

What is claimed is:

1. A voltage control circuit comprising a power su-pply, having a switching means for deactivating said power supply, a current storage means coupled across said power supply, a traveling wave tube having a cathode to collector path coupled across said power supply, said traveling wave tube being susceptible of arcing, a thyratron having a control terminal and having a current path coupled .across said power supply, a blocking oscillator coupled to said cathode to collector path of said traveling wave tube and to said control termin-al of said thyratron, said blocking oscillator responding to an arcing condition to initiate said thyratron into conduction so that said current path discharges said current storage means of said power supply to lower the voltage across said traveling wave tube so as to remove said arcing and to bias said thyratron out of conduction, `and a memory circuit including a capacitor coupled to said current path of said thyratron and to a source of reference potential for being charged when said thyratron is conductive and including a series coupled coil of a relay `and la gas tube coupled across said capacitor for passing current through said coil of said relay when said capacitor charges a predetermined amount, said relay coupled ,to said switching means of said power supply for deactivating said power supply when said capacitor charges said predetermined amount.

2. A voltage control system for controlling voltage vfrom a source of power applied to a traveling wave tube,

said traveling wave tube including a cathode to collector path coupled across said source of power, the system having a storage capacitor coupled across the output terminals of ysaid power supply comprising a thyratron having an anode to cathode path coupled across said .source of power and having a grid, a sensing resistor coupled in the cathode to collector path of said traveling wave tube for developing a signal during the occurrence of an are in said traveling wave tube, a blocking oscillator coupled between said sensing resistor and the grid of said thyratron for initiating conduction of said thyratron in response to said signal from said sensing resistor, a biasing resistor coupled in ythe anode to cathode path of said thyratron, a diode coupled to the anode -to cathode path of said thyratron between said biasing resistor and said thyratron, a charging capacitor coupled between said diode andan output terminal of said power supply, a gas tube and a relay having a coil with said gas tube and coil coupled in series across said charging capacitor, and switching means coupled to said sou-ree of power and to said relay for disconnecting said source of power when said charging capacitor charges to a potential to bias said gas tube into conduction.

3. A voltage control system comprising a source of power having iirst and second output terminals and having a path for applying power thereto, a storage capacitor coupled across said output terminals, a traveling wave tube having a collector to cathode path coupled respectively across said tirst and second output terminals, a thyratron having a control grid and having an anode and a cathode coupled across lsaid first and second output terminals to form a current path, current sensing means coupled -in the collector to cathode path of said traveling wave tube between the cathode and said second terminal of said source of power, a blocking oscillator having an input terminal coupled to the cathode of said traveling -wave tube and having an output terminal coupled to the .control grid or" said thyratron, a signal forming resistor coupled in the current path between the cathode of said thyratron and said second output terminal of said source of power, a diode having an cathode and having an anode coupled to the cathode of said thyratron, variable resistance means having one end coupled to the second terminal of said source of power, a charging capacitor coupled between the cathode of said diode and the other end of said variable resistance means, relay means having a coil with one end coupled between said diode and said charging capacitor, and 4a gas tube coupled from between the other end of said coil to between said charging capacitor and said resistance means.

4. A voltage control circuit comprising a source of voltage having a positive and a negative supply terminal and a path to said supply terminals, current storage means coupled between said positive and negative supply terminals, a gas tube having an anode coupled to said positive supply terminal, a cathode coupled to said negative supply terminal to form a current path and having a grid, a load subject to arcing shorts and including signal forming means to develop an overload signal in response to an arcing short, pulse forming means coupled to said signal forming means and coupled to said control grid of said gas tube for responding to said overload signal to apply a pulse having a fast rise time to the control grid of said gas tube so as to initiate said gas tube into conduction and discharge said current Vstorage means to reduce the potential across said load for removing said arcing short and to reduce the potential between the anode and cathode of said gas tube for biasing said gas tube out of conduction, a diode coupled to the cathode of said gas tube, a cathode resistor coupled in said current path between the cathode of said gas tube and said negative supply terminal, a variable resistance coupled to said negative supply terminal, a charging capacitor coupled between said diode and said variable resistance, `a relay having a coil with a first and a second end with one end coupled to between said diode and said charging capacitor, means responsive to a predetermined potential diiference across a rst and a second terminal thereof to be biased into conduction and having said iirst terminal coupled to the second end of said coil and said second terminal coupled between said charging capacitor and said variable resistance, and switching means coupled in said path of said source of voltage and to said relay for disconnecting the voltage across said supply terminals when said capacitor charges so as to bias 4said means responsive to a predetermined potential difference into conduction.

5. A voltage control circuit to protect a load against arcing shorts in a current path therethrough having first and second ends, comprising a power supply coupled to the first and second ends of said current path across said load and having a switching means for deactivating said power supply and a current storage means coupled across said power supply, a thyratron having a control terminal and having a current path coupled across said power supply, a lblocking oscillator coupled to the current path of said load and to said control terminal of said thyratron, said blocking oscillator responding to an arcing short to initiate said thyratron into conduction so that the current path thereof discharges said current storage means of said power supply and lowers the voltage across said load so as to remove said arcing short and to bias said thyratron out of conduction, and a memory circuit including a capacitor coupled to said current path of said thyratron and to a source of reference potential for being charged when said thyratron is conductive and including a series coupled coil of a relay and a gas tube coupled across said ycapacitor for passing current through said coil of said relay when said capacitor charges a predetermined amount, said relay coupled to said switching means of said power supply for deactivating said power supply when said capacitor charges said predetermined amount.

6. A voltage control circuit to protect a load against arcing shorts in a path therethrough between irst and second terminals comprising a, power supply coupled between the rst and second terminals of said load and having a switching means for deactivating said power supply and a current storage means coupled across said power supply, control means having a current path coupled across said load and having a control terminal for initiating said control means into conduction in response to a control signal and a potential dierence at the ends of `said current path, said control means being normally nonconductive, said control means after being initiated into conduction, remaining in conduction until the potential difference at the ends of said current path decreases to a predetermined value, a blocking oscillator coupled to the second terminal of the path through said load and to said control terminal of said control means, said blocking oscillator responding to an arcing short to initiate 4said control means into conduction so that the current path through said ycontrol means discharges said current storage means of said power supply to lower the voltage across said load, remove said arcing short and decrease the voltage across the current pathvof said control means to said predetermined value to bias said control means out of conduction, and a memory circuit including a capacitor coupled to said current path of said control means and to a source of reference potential for being charged when said control means is conductive and including a series coupled coil of a relay and a gas tube coupled across said capacitor for passing current through said coil of said relay when said capacitor charges a predetermined amount, said relay coupled to said switching means of said power supply -for deactivating said power supply when said capacitor charges said predetermined amount.

w References Cited in the le of this patent UNITED STATES PATENTS 2,575,232 Parker Nov. 13, 1951 2,659,008 Floyd Nov. 10, 1953 2,733,338 Alsmeyer Jan. 31, 1956 2,815,446 Coombs Dec. 3, 1957 2,845,529 Weldon July 29, 1958 2,882,445 Sprengeler et al. Apr. 14, 1959 

5. A VOLTAGE CONTROL CIRCUIT TO PROTECT A LOAD AGAINST ARCING SHORTS IN A CURRENT PATH THERETHROUGH HAVING FIRST AND SECOND ENDS, COMPRISING A POWER SUPPLY COUPLED TO THE FIRST AND SECOND ENDS OF SAID CURRENT PATH ACROSS SAID LOAD AND HAVING A SWITCHING MEANS FOR DEACTIVATING SAID POWER SUPPLY AND A CURRENT STORAGE MEANS COUPLED ACROSS SAID POWER SUPPLY, A THYRATRON HAVING A CONTROL TERMINAL AND HAVING A CURRENT PATH COUPLED ACROSS SAID POWER SUPPLY, A BLOCKING OSCILLATOR COUPLED TO THE CURRENT PATH OF SAID LOAD AND TO SAID CONTROL TERMINAL OF SAID THYRATRON, SAID BLOCKING OSCILLATOR RESPONDING TO AN ARCING SHORT TO INITIATE SAID THYRATRON INTO CONDUCTION SO THAT THE CURRENT PATH THEREOF DISCHARGES SAID CURRENT STORAGE MEANS OF SAID POWER SUPPLY AND LOWERS THE VOLTAGE 